Deep Arctic gas hydrate mounds host ultra deep cold seep ecosystem

by Robert Schreiber
Berlin, Germany (SPX) Dec 26, 2025

A multinational research team led by UiT The Arctic University of Norway has identified the deepest known gas hydrate cold seep on Earth during the Ocean Census Arctic Deep - EXTREME24 expedition, documenting the Freya Hydrate Mounds at 3,640 meters depth on the Molloy Ridge in the Greenland Sea. The work reveals a previously unknown ecosystem on the Arctic seafloor where exposed gas hydrate, methane-rich fluids, and seep-associated fauna shape a structured environment with implications for Arctic governance and sustainable development.

The Freya Hydrate Mounds host active methane seepage, crude oil emissions, and chemosynthetic communities adapted to hydrocarbon-rich fluids at hadal depths. The team reports that these deposits extend the known depth range of gas hydrate outcrops by nearly 1,800 meters beyond the more common occurrences at less than 2,000 meters, prompting a reassessment of where such systems can form and persist in polar basins.

"This discovery rewrites the playbook for Arctic deep-sea ecosystems and carbon cycling," said Giuliana Panieri, Professor at UiT and now Director of CNR-ISP, and Chief Scientist of the expedition, together with Alex Rogers. "We found an ultra-deep system that is both geologically dynamic and biologically rich, with implications for biodiversity, climate processes, and future stewardship of the High North."

"There are likely to be more very deep gas hydrate cold seeps like the Freya mounds awaiting discovery in the region, and the marine life that thrives around them may be critical in contributing to the biodiversity of the deep Arctic" said Jon Copley of the University of Southampton, UK, who led the biogeographic analysis of the new discovery. "The links that we have found between life at this seep and hydrothermal vents in the Arctic indicate that these island-like habitats on the ocean floor will need to be protected from any future impacts of deep-sea mining in the region."

High-resolution remotely operated vehicle imagery shows partially collapsed gas hydrate mounds in the Molloy Deep, where exposed hydrates lie beneath sediment cover and support dense fields of frenulate worms, crustaceans, and small carbonate crusts. Fractures and structural failure within the mounds reflect the destabilizing effect of hydrate buoyancy and changing pressure-temperature conditions that can lead to progressive collapse.

Key findings from the Freya Hydrate Mounds include the documentation of hydrate deposits at 3,640 meters, far deeper than typical hydrate outcrops, and the observation of methane gas flares rising more than 3,300 meters through the water column. These tall flares rank among the highest reported globally and indicate focused fluid flow, while geochemical signatures show that thermogenic gas and crude oil originate from Miocene-aged sediments, evidencing long-lived deep fluid migration.

The ecological data reveal chemosynthetic communities dominated by siboglinid and maldanid tubeworms, snails, amphipods, and other invertebrates that rely on chemical energy from seeping fluids. Substantial overlap between fauna at Freya and communities near Arctic hydrothermal vents points to ecological connectivity between seep and vent habitats across the deep Arctic seafloor.

The hydrate mounds appear in different stages of growth, destabilisation, and collapse, demonstrating that the system evolves through cycles of hydrate formation, dissociation, and sediment reworking rather than remaining static structures. This dynamic behaviour, captured with advanced ROV imaging, shows how tectonics, heat flow, and ocean conditions can alter mound integrity and seepage pathways over time.

Freya provides an ultra-deep natural laboratory for investigating methane behaviour in the water column and the potential impacts of changing waters entering the Arctic through gateways such as the Fram Strait. Tracking hydrate stability and seepage at these depths can improve understanding of how deep carbon reservoirs respond to environmental change and how much methane may be transferred to overlying waters.

"These are not static deposits," Panieri added. "They are living geological features, responding to tectonics, deep heat flow, and environmental change."

The discovery comes at a time of increased international attention on the Arctic Ocean and its seabed resources, as ultra-deep environments are being considered for future resource exploration. The authors argue that evidence-based environmental assessments, detailed baseline studies, and long-term monitoring of seep activity, fluid fluxes, and faunal change will be essential to guide decisions affecting these deep habitats.

In their assessment, the scientists emphasize that sites such as Freya clarify how geological processes and biological communities interact across the Arctic deep sea and how these interactions may shift under natural variability and human-driven pressures. "Understanding these unique habitats is essential for safeguarding biodiversity and supporting responsible decision-making in polar regions," Panieri noted.

Research Report:Deepest gas hydrate cold seep ever discovered in the Arctic: international research team unveils Freya hydrate mounds at 3,640 m depth